Repeater systems are typically used to extend the range of a radio frequency communications signal and to fill nulls in the intended coverage area of the transmitting antenna. Nulls are regions that are blocked from receiving radio frequency (RF) signals. Nulls are caused by hills, trees, structures, buildings, etc.
A typical repeater system comprises three basic parts: a link antenna which is directed/aimed at the transmitting antenna; repeater electronics; and a broadcast antenna which is directed towards the area of interest. Often, the link antenna is highly directive (high gain) with a very narrow beamwidth since it only needs to “see” the transmitting antenna. The broadcast antenna has a larger beamwidth which is determined by the intended area to be covered. The repeater electronics may contain an assortment of filters, splitters, and RF amplifiers.
Two primary performance factors for coverage on which an antenna system is based are gain and output power. The output power is primarily determined by the sum of the link and broadcast antenna gains and the maximum (linear) output power of the amplifier(s). The system gain is determined by the sum of the passive antenna gains, plus the gain of the amplifier(s). This is limited by the isolation (or mutual coupling) between the broadcast and link antennas. The isolation depends on the antenna type, front to back (F/B) ratio, beamwidth and antenna placement/separation.
Repeater systems are used in a variety of applications such as TV and radio transmission, cellular/PCS communications, and positioning systems. Existing positioning systems, such as the Global Positioning System (GPS), use transmitting antennas mounted on satellites. The GPS antennas require a clear line-of-sight between them and their receivers. In other words, a GPS receiving antenna must have an unobstructed view of the sky such that a minimum number of GPS satellites are always in view at any particular time. Consequently, accurately determining the position of a GPS receiver requires the GPS receiving antenna to be in the line-of-sight of these GPS transmitting antennas at all times. Therefore, when a person with a GPS receiver enters a structure such as a building, a car garage, a tunnel, etc., the GPS signal is lost. This is a particularly troublesome problem in light of a new FCC mandate.
Specifically, the FCC has mandated that wireless communications systems (e.g., cellular and PCS) must provide Enhanced 911 service. This mandate requires that persons making wireless 911 calls be located to within 125 meters of their actual location. The mandate also requires locating such persons with a 67% reliability. Currently, a commercial version of the GPS is being considered as an approach to providing the required location information. The commercial GPS being considered uses the Standard Positioning System (SPS). The SPS is 95% accurate in providing the location of a GPS receiver to within 100 meters horizontally and 156 meters vertically of the actual GPS receiver location.
However, a major deficiency with using the GPS for the mandated Enhanced 911 service is the inability of GPS receivers to determine location information when their antennas do not have a clear line-of-sight with the satellites. For example, GPS receivers are blocked from communicating with GPS satellites when the receivers are inside a structure such as a building, a car garage, a tunnel, etc. Since many wireless users spend a significant amount of time inside structures, this represents a major problem in trying to meet the 67% reliability requirement.
Therefore, there is a need for a repeater capable of retransmitting a GPS signal inside a structure such that an uninterrupted GPS signal can be transmitted to the GPS receiver. The present invention is directed to addressing this need.